As an educator, I feel it important to model lifelong learning for my students. I've used the following tools to build a personal learning network (PLN) online. My PLN is a way to collaborate with peers, mostly educators, from around the world.
Twitter is a "microblogging" tool. Think of it as a cross between a chat and a blog. Tell or ask your group anything, but keep it to 140 characters or less.
Nings are social networks built around specific interest areas. I've joined quite a few, and you can easily create your own. A great one to start - Classroom 2.0.
Diigo is a social bookmarking tool. It allows me to bookmark all of my favorite sites online and tag them for later sorting and sharing. Diigo also allows users to create and participate in groups with common interests. Users can also create/share lists of links. I install the toolbar on every computer I use, Mac or Windows, usually in Firefox. Check out the Teaching with Tablets Group.
Great tool to manage RSS Feeds. Start a Google Account first. This gives you Gmail (great way to manage junk mail if you don't use it for anything else) and access to iGoogle toolbars. It also gives you access to Google Docs.
There are tons of messaging tools online, but this one is universal. It's great as a chat tool, especially for those who like to actually hear a voice and/or see a face on the other end.
Other great tools to keep in your toolbox...